This question is really just to satisfy my curiosity. I am currently using a 3 piece airlock, but what about a one way check valve?
I have heard that sometimes primaries can suck the sanitized water/vodka through the airlock back into the fermenter. Why not use a one way check valve so nothing can get in, but the gas can escape? With check valves there is a certain amount of pressure that needs to be built up before they release any gas; the same principle goes with an airlock.
I assume the pressure needed for a check valve is greater than a traditional airlock and that this is why airlocks are preferred? But we all know what ASSuming can do.